1. Field of the Invention
This invention relates to a granular fertilizer with a decomposable coating and a process for producing the same. More particularly it relates to a granular fertilizer with a decomposable coating containing a poly-3-hydroxy-3-alkylpropionic acid as an indispensable component thereof and if necessary, a light-decomposable resin, and a process for producing the same.
As to the coating of the fertilizer of the present invention, the 3-hydroxy-3-propionic acid polymer contained in the coating is decomposed mainly by microorganisms in the soil, while the photo-degradative resin component contained in the coating is degraded mainly by light on the surface layer of the soil hence after application of the product of the present invention, the coating remains neither in the soil nor on the surface layer of the soil. Further, it is possible to add various adjuvants or agents to the coating of the present invention for adjusting the dissolving-out of the granular fertilizer.
2. Description of the Related Art
Various researches have so far been made in order to cause the dissolving-out of the fertilizing component contained in granular fertilizers applied to the soil to correspond to the needs of crops accompanying their growth, or in order to prevent the moisture absorption or caking of granular fertilizers during their current process. One of such researches is directed to a process of coating the surface of granular fertilizers with high-molecular compounds. For this coating, either of thermosetting or thermoplastic resins have been used. However, coating with such high-molecular compounds has raised various problems as described below.
As to processes using thermosetting resins, the following resins have been disclosed:
for example, styrenized alkyld resins and phenolic resins (British patent No. 954,555), fatty oil-modified alkyd resins, fatty oil-dicyclopentadiene copolymers and diisocyanate-modified fatty oil polymers (Japanese patent publication No. Sho 40-28,927/1965), phenolic resins (Japanese patent publication No. Sho 44-28,457/1969), etc.
Further as to processes using thermoplastic resins, the following resins have been disclosed:
for example, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyethylene and polyfluorinated alkanes or copolymers consisting of two or more constituting unit monomers of the foregoing (British patent 815,829) and emulsion-polymerized vinyl acetate liquid (Japanese patent publication No. Sho 37-15,832/1962).
When high-molecular compounds, particularly thermoplastic resin solutions or their emulsion-polymerized liquids are used as the coating material, the following problem has been raised:
Japanese patent publication No. Sho 42-13,681/1967 discloses that when the surface of granular products are coated with a liquid resin or a stringing resin, coating with only several percentages of such resins causes particles to adhere to one another to form a block, not individual granules; hence uniform and thick coating is difficult.
Japanese patent application laid-open Nos. Sho 50-99,858/1975, Sho 51-75,674/1976 and Sho 53-98,265/1978, each directed to a process for coating granular fertilizers, previously invented by the present inventors, disclose that the properties of the resin solution and choice of drying conditions cause no blocking during the coating process and coating is effected by way of a simple process and efficiently.
Japanese patent application laid-open No. Sho 50-99,858/1975 discloses a process for coating granular fertilizers wherein, when granular fertilizers are coated with a coating material composed mainly of polyolefins, a solution of the coating material is sprayed on granular fertilizers and at the same time with the coating, the coated material is dried by a high speed hot air stream. The specific feature of the process consists in that (1) it is possible to have an extremely thin and uniform coating and also (2) it is possible to adjust the dissolving-out rate of the fertilizing component by dispersing a surfactant as an agent for adjusting the dissolving-out rate in the coating.
Japanese patent application laid-open No. Sho 51-75,674/1976 discloses that vinylidene chloride polymer resins and an ethylene-vinyl acetate copolymer, the vinyl acetate content of which is 5% by weight or less, can coat granular fertilizers uniformly and extremely thinly as in the case of use of polyolefin resins.
Japanese patent publication No. Sho 60-37,074/1985 discloses that coating of granular fertilizers with polyolefin resins, ethylene-vinyl acetate copolymer and a surfactant can control the dissolving-out of the fertilizing component with a high stability.
Further, Japanese patent publication No. Sho 60-3,040/1985 and Japanese patent application laid-open No. Sho 55-1,672/1980 disclose that when mineral powder such as talc or sulfur is dispersed in the coating of the above-mentioned polyolefin resins, etc., the function of controlling the dissolving-out is kept and also the degradation and decomposition of the remaining capsule after the dissolving-out are promoted.
Such a series of coating techniques developed by the present inventors have been further developed and practically employed for coating granular urea or chemical compounds and the resulting products have come to be broadly used as fertilizers superior in control of the dissolving-out. As to these fertilizers, while the dissolving-out can be continuously controlled over several hours to several years without varying the thickness of the coating, the dissolving-out basically exhibits a slow-release pattern and the capsule remaining after the dissolving-out of the fertilizing component is deteriorated or decomposed by light or oxygen. However, appearance of a coated granular fertilizer has been desired by the consumers, which fertilizer is of the slow release type coated with a more microorganism-decomposable material or those of time capsule type, the capsule of which is rapidly decomposed by microorganisms after the dissolving-out of the fertilizing component.
In view of these situations, the present inventors have done extensive research directed to a slow-release type fertilizer which is based on a microorganism-decomposable material and optionally controllable and a time capsule type fertilizer which does not dissolve out during a definite period, but thereafter dissolves out during a short period, and as a result have found the present invention.
We have confirmed that poly 3-hydroxy-3-alkylpropionic acids, particularly those wherein the alkyl group thereof is methyl or ethyl, are microorganism-decomposable, and, in order to carry out the present invention, the polymers have been dissolved in various solvents and coating has been carried out with solutions. In the case of some of the solvent solutions that were added in spray form, the coating material became adhesive and particles during the coating adhered to one another; hence it was impossible to coat single particles. Further, in the case of others, a tough coating specific of high-molecular compounds could not be obtained. As a result of trial and error, according to the following process referring to a coating process invented by the present inventors and disclosed in Japanese patent application laid-open No. Sho 50-99,858/1975, it has been possible to uniformly coat single particles; thus the process of the present invention has been found.
In order to complete these techniques, a high-molecular material satisfying all of the following (1) to (5) should be found:
(1) the material is a tough high-molecular material which is easily decomposed by soil microorganisms; PA0 (2) it is possible to develop a coating-process technique wherein the material is used; PA0 (3) the product obtained by coating process with the material can control the dissolving-out; PA0 (4) when the material is made composite with other materials, it is possible to control the dissolving-out rate within a broad range; and PA0 (5) even under conditions where the material is attacked by soil microorganisms in the soil, control of the dissolving-out is possible. PA0 (1) A granular fertilizer with a decomposable coating comprising a poly 3-hydroxy-3-alkylpropionic acid as an active ingredient. PA0 (2) A granular fertilizer according to item (1) wherein said alkyl is methyl group or ethyl group. PA0 (3) A granular fertilizer according to item (1) wherein said decomposable coating comprises said poly 3-hydroxy-3-alkylpropionic acid and at least one member selected from the group consisting of as resins, polyvinylidene chloride, olefin polymer resins, rubbery resins, ethylene-vinyl acetate copolymer, polystyrene, polymethyl methacrylate, ethylene-carbon monoxide copolymer, ethylene-vinyl acetate-carbon monoxide terpolymer, ethylene-ethyl acrylate copolymer and ethylenemethacrylic acid copolymer and as low molecular resinous substances, paraffin, hardened oils, solid fatty acids, metal salts thereof, beeswax, Japan wax, petroleum resins and rosins. PA0 (4) A granular fertilizer according to item (1) wherein said decomposable coating further comprises an inorganic or organic, difficultly water-soluble or water-insoluble powder. PA0 (5) A granular fertilizer according to item (3) wherein said decomposable coating further comprises an inorganic or organic, difficultly water-soluble or water-insoluble powder. PA0 (6) A granular fertilizer according to item (4) wherein said inorganic powder is powder of talc, clay, silica, diatomaceous earth, metal oxides or sulfur and said organic powder is powder of starch or crotylidene diurea. PA0 (7) A granular fertilizer according to item (5) wherein said inorganic powder is powder of talc, clay, silica, diatomaceous earth, metal oxides or sulfur and said orgnaic powder is powder of starch or crotylidene diurea. PA0 (8) A process for producing a granular fertilizer with a decomposable coating which process comprises adding an organic solvent solution of a poly 3-hydroxy-3-alkylpropionic acid to a granular fertilizer in fluidized state in the form of spray, and when added, blowing a high speed hot air stream onto said granular fertilizer to thereby instantaneously remove the solvent contained in said organic solvent solution and also dry the resulting fertilizer. PA0 (9) A process according to item (8) wherein in said organic solvent solution are dissolved said poly-3-hydroxy-3-alkylpropionic acid and at least one member selected from the group consisting of as resins, polyvinylidene chloride, olefin polymer resins, rubbery resins, ethylene-vinyl acetate copolymer, polystyrene, polymethyl methacrylate, ethylene-carbon monoxide copolymer, ethylene-vinyl acetate-carbon monoxide terpolymer, ethylene-ethyl acrylate copolymer and ethylene-methacrylic acid copolymer and as low molecular resinous substances, paraffin, hardened oils, solid fatty acids, metal salts thereof, beeswax, Japan wax, petroleum resins and rosins. PA0 (10) A process according to item (8) wherein in said organic solvent solution is further mixed and dispersed an inorganic or organic, difficultly water-soluble or water-insoluble powder. PA0 (11) A process according to item (9) wherein in said organic solvent solution is further mixed and dispersed an inorganic or organic, difficultly water-soluble or water-insoluble powder. PA0 (12) A process according to item (10) wherein said inorganic powder is powder of talc, clay, silica, diatomaceous earth, metal oxides or sulfur and said organic powder is powder of starch or crotylidene diurea.
At the initial stage of such investigate research, various high-molecular materials were investigated and chosen, and evaluation was made as to whether or not the materials embedded in the soil were decomposed by soil microorganisms. As a result it has been found that among the high-molecular materials, several kinds were decomposed. Various coating processes were examined using these decomposable materials. However, it was impossible for most of the materials to carry out a uniform coating process endurable to control of the dissolving-out. Even in the case of materials by the use of which a coating process affording a uniform coating was possible, most of these materials could not be practically used in view of evaluations of the physical properties of the coating and test of dissolving-out in water.
It has been confirmed by a test of dissolving-out in water that when materials screened here are combined with other materials and the combinations are used as a composite material, such a composite material can control the dissolving-out rate within a broad range.
These materials were further subjected to a test of dissolving-out in the soil under conditions where they were decomposed by soil microorganisms.
When these materials were converted into composite materials, for example if high-molecular materials were occupied by a large proportion of a microorganism-non-decomposable high-molecular material, some of the materials were found to inhibit the decomposition of the capsule itself in the soil, but these have been usable as the current slow-release type dissolving-out fertilizers. As described above, the present invention has been achieved as a result of research and development directed to various technical problems over a long time.